Process for the continuous production of steel from ore

ABSTRACT

Iron ore is continuously converted to steel by introducing the ore into a shaft furnace of substantially equal cross-sectional width and thus forming a column of the charge therein; introducing a reducing gas into the furnace and exposing the bottom portion of the charge column from below to the heat of an electric arc the source of which is centrally disposed in the bottom of the furnace and thus causing the gradual super-heating and melting of the bottom portion of the charge so as to form a dome-shaped cavity at the bottom of the charge column while the column gradually moves downward under the force of gravity and collecting and tapping the formed molten steel at the bottom of the furnace.

[451 July 15, 1975 FOREIGN PATENTS OR APPLICATIONS .9l 1.994 9/l970Germany 75/44 S Primary Examiner-P. D. Rosenberg Attorney, Agent, orFirmMichael S. Striker [57] ABSTRACT Iron ore is continuously convertedto steel by introducing the ore into a shaft furnace of substantiallyequal cross-sectional width and thus forming a column of the chargetherein; introducing a reducing gas into the furnace and exposing thebottom portion of the charge column from below to the heat of anelectric arc the source of which is centrally disposed in the bottom ofthe furnace and thus causing the gradual su per-heating and melting ofthe bottom portion of the charge so as to form a dome-shaped cavity atthe bottom of the charge column while the column gradually movesdownward under the force of gravity and collecting and tapping theformed molten steel at the bottom of the furnace.

.. 75/11; 75/12; 75/44 5 0220 7/00; C2lc 7/00 75/38, 40. 43, 44 5, l0,75/11 PROCESS FOR THE CONTINUOUS PRODUCTION OF STEEL FROM ORE Inventor:Hans-.luergen Langhammer,

Bremen, Germany Assignee: Klockner Werke AG, Duisburg,

Germany Filed: Mar. 2, 1973 Appl. No.: 337,738

Foreign Application Priority Data Mar. 4, l972Germany.,,......,.,...,............

U.S. Cl. Int. Cl. Field of Search..........

References Cited UNITED STATES PATENTS United States Patent Langhammer20 Claims, 1 Drawing Figure WV4/MUMW/ (N wwM U J H W w H a, so OM00, ,0so 8 6%,? o 00 0 MW 000 00 on m o o o 00 0 o so, si n? a e m a ao O ww ww O O00 O O O. a

can an 0 w%% o o OwOoo m s O O w 0 3050mm? /4 0% OwO O O M B o o w OM 5O O 7 00 w 000 m Estes Geck Krause PROCESS FOR THE CONTINUOUS PRODUCTIONOF STEEL FROM ORE BACKGROUND OF THE INVENTION The invention relates to acontinuous process for making steel from ore, pellets, sinter, etc. in ashaft furnace.

Reduction processes are known under the general term direct reductionprocesses whereby ore or pellets are converted to iron and sponge iron.These processes are carried out in various types of apparatus. Bestknown is the direct reduction process of coarse ores or pellets in ashaft furnace or of fine ore and coal (for instance coke) in a rotaryfurnace. The final product is sponge iron which usually has a residualcontents of unreducible oxygen and in addition contains, in the form ofcontaminations gangue components of the ore which are not amenable toreduction.

This intermediate product is therefore then usually subjected to asecond independent operation where it forms, so to speak, the startingproduct for scrap iron in the conventional steel production apparatus.Unfavorable in this stage however is the high porosity, that is largesurface, which causes a tendency to reoxidation. Extended unprotectedstorage and melting methods under oxidizing conditions therefore have anundesirable effect.

For the latter reason it is customary to melt down sponge iron formed ina direct reduction process in electro-furnaces. In theseelectro-furnaces the sponge iron is preferably fed into the furnace in acontinuous charge as distinguished from the conventional discontinuousbucket charge.

It is therefore an object of the invention to provide for a processwherein sponge iron which has been produced as customary in a shaftfurnace can be melted down in the same apparatus in a continuousoperation and can be discharged as steel.

SUMMARY OF THE INVENTION According to the basic concept of the inventiona charge column is formed in the shaft furnace which after reduction byreducing gas is exposed from its bottom side to a centrally arrangedelectric arc. the heat of which covers most of the cross section of thebottom portion of the column. In this form the bottom portion issubjected to melting and super-heating thus forming a domed cavity theroof of which supports the charge column while the column graduallymoves down under the force of gravity.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing in adiagrammatic form shows a shaft furnace for use in the method of theinvention in cross-sectional view.

DETAILS OF THE INVENTION AND PREFERRED EMBODIMENTS The invention permitsthe melting of the sponge iron and conversion to steel in the same shaftfurnace in which the sponge iron has been made from the original orev Inaddition it avoids the two step process consisting of a reduction stageand a melting and steel conversion stage and permits the melting processwhich is at present carried out discontinuously to be effected in acontinuous operation.

The process results in considerable saving in heat supply and energybecause the usual cooling down of the sponge iron from the temperatureof the reduction stage and the subsequent reheating up to the meltingstage is carried out in one and the same process and without anyintermediate cooling between the two stages. Besides reoxidation can beavoided by melting the sponge iron under reducing conditions immediatelyafter the reduction. Furthermore all apparatus for discharging andsupplying the iron ore from the reduction stage and transferring it intothe melting stage can be dispensed with. In addition all necessaryadditives for the final steel composition can be added simultaneouslywith the ore and partly even in the form of oxides.

A specific embodiment of the invention provides for the introduction ofthe reducing gases in part peripherally to the charge column and in partdirectly into the melting cavity which forms during the process so thatthe latter gas there is subject to additional heating.

Another embodiment of the invention contemplates sealing of theapparatus and thus maintaining of a reducing atmosphere by introducingadditional reduction gas or an inert gas through a gap formed around theseat of the electrode in the floor of the furnace.

It is preferred to add all alloy components which are necessary for thefinal steel composition in a uniform and continuous operation during theprocess. Furthermore the limestone for the gangue or the coal or cokefor the alloy or for the reduction step and reducible alloy oxides canlikewise be introduced in a continuous and uniform operation during theentire process.

It is furthermore possible in the process of the invention tointerconnect the melt performance, that is the supply of heat by meansofa specific amount of electric energy, and the amount of introducedreduction gas.

The process of the invention causes the burning out of a dome-shapedcavity under the action of the heat of the electric arc. The surface ofthe dome then is subject to gradual melting in the form of an invertedbowl and continuously reforms under the action of the downwardly movingcharge column which is caused to move by the force of gravity.

The portions of the sponge iron which are in the reduction zone directlyabove the bottom portion of the charge column will gradually be weldedtogether prior to being molten. This occurs under the action of thedownwardly increasing temperature. The welding together of the ironparticles will occur at their contact points and thus a firm supportstructure of arch-shaped design will form at the lower end of the chargecolumn. This vault structure has sufficient strength to support thecharge column lying above and to reform itself by a continuous process.

By introduction of part of the reducing and fuel gases from the outsidein a peripheral direction and introducing part of the gases directlyinto the melt cavity it is possible to superheat the reduction gasesdirectly or indirectly by the heat of the electric arc. The amount ofheat thus absorbed is then passed on in countercurrent to the higherportions of the change column and is taken up in the reduction process.

The invention contemplates that the reduction gases may also beintroduced through a gap between the adjustable electrode structure forthe electric arc and a dam-like elevation formed in the bottom of thefurnace. This dam thus forms an annular basin of which the inner wall,that is the wall portion surrounding the aperture of the ring structuresurrounds the electrode leaving a gap between the wall and theelectrode. By introduction of the reducing gases through this gap or ifdesired by an inert gas the electrode itself is protected against metalsplattering from above. Besides this structure also helps to maintainthe reducing atmosphere particularly since the chimney effect of theshaft furnace system by itself has an efficient sealing effect againstexterior air entry.

Contrary to conventional steel production processes substantial savingsare possible in the refractory lining of the furnace. The accumulatingmetal which flows down from the column constitutes itself a protectionof the floor of the furnace and the column itself protects the sidewalls. Only the dam-like elevation around the electrode is exposed tothe heat of the electric arc. All other refractory portions of thefurnace are protected against overheating by means of either liquid orsolid metal.

It is therefore possible to make only the bottom por tion of the furnacefrom high quality refractory materials. All other portions of the shaftdo have to withstand only the comparatively low temperature attach ofthe reduction gas. This means that the larger part of the furnace can beformed of fire clay type materials while only the lowermost portionshould be made of basic magnesite or dolomite or of an acidic refractorywhich has a high alumina contents.

The continuous operation results in a high performance relative to thesurface of the hearth or total furnace space, which compared with theconventional discontinuous steel production process requires onlycomparatively small furnaces and thus a reduced cost in investment andmaintainance.

The continuous operation and the complete envelop ing of the heat sourceby the melting metal result in ideal heat transfer conditions whichcontrary to the discontinuous steel production processes do notdeteriorate in the course of the conversion of a particular charge. Thispermits to increase the comparatively high heat effect of above 70% asit is obtained in the melting process in the electro-furnaces in case ofthe discontinuous operation to an amount in excess of 90% with thecontinuous operation of the invention. This is possible because the onlyloss of heat in this case will occur through the wall and this can beavoided by sufficient insulating materials.

The invention also embraces an apparatus for carrying out the process.Broadly, the apparatus comprises a shaft furnace which is open at theupper end and which has a floor through which an electrode penetrateswhile an annular gap is formed around the electrode. The shaft furnacehas a substantially equal crosssectional width or has at most a widthwhich increases slightly towards the bottom. It has smooth wallportions, that is all protruding or direction changing extensions of theinner wall are avoided, to permit the uniform and continuous movement ofthe charge column under the action of gravity.

It is important also in the apparatus that a dam-like elevation at thebottom made of refractory material forms a basin for the molten steeland thus separates the adjustable arc electrode from the steel.

As already indicated it is a further characteristic of the apparatusthat only the lowermost shaft portion which is directly exposed to theheat of the electric arc is lined with high quality refractory materialwhile the remainder is formed only of regular refractories.

A specific embodiment also contemplates that the tap hole is in the areaexposed to the heat of the electric arc. The height of the dam-likeelevation will determine the depth of the sump or basin for the metal onthe floor. Thus the residence time and amount of heating exposure can beadjusted as desired by changing the height of the dam-like elevation.

It is also preferred that the tap hole and the connection to a receivingtank for the molten steel be sealed against the effects of exterioroxidizing atmosphere.

With reference to the drawing which shows a particular embodiment of theapparatus it will be seen that 1 is a shaft furnace which is in itsupper portion is filled with ore and alloying elements and conventionaladditives. Electrode 4 penetrates through the floor 3 of the furnace. Anannular gap 5 is formed around the electrode. Through the gap, reducinggas, for instance natural gas, may be blown into the melt space 12. Thusthe reducing gas is heated by the are 6 emanating from the electrode andwill flow in countercurrent to the charge column 2. Further reducinggas, for instance natural gas, may be introduced through the peripheralopenings 7 into the charge column.

The ore is thus converted to sponge iron in the lower part of the chargecolumn, that is in the part which is opposite the electric arc. Thesponge iron particles will be welded together at their multiple pointsof contact. Thus a firm support structure for the charge column 2 willbe formed. The steel 8 which accumulates on the floor of the furnace isdischarged through a tap hole 9. The wall-shaped elevation 10 on thefloor surrounds the electrode and thus prevents the liquid steel frompenetrating into the gap 5 between the electrode and the floor.

In the illustrated embodiment, the lower wall portion 13 of the furnace1 comprises a high-quality refractory material while the upper wallportion 11 comprises a regular refractory material.

EXAMPLE In order to perform the method according to the invention ore inform of pellets, having a metallic iron content of 679%, is used. Thisore consists of 96% Fe O and 4% SiO and impurities. The ore-column ispreheated to 900 C by means of hot reducing gases. The reducing gasesconsist of 49,2% H 43,6% CO,

CO2, H20, 2,370 CH4 and N2.

By means of this reducing gas the ore is reduced to sponge iron,consisting of 94,8% metallic iron, 1,35% SiO and 3,85% 0 and impurities.

For the production of 1000 kg metallic iron 1396 kg ore (pellets), 50 kglime and l530 Nm reducing gas are needed. 20% of the reducing gas areadmitted through the annular gap, being formed around the electrode.

The energy being necessary for heating and melting from 900 to l600 Camounts to 268 kWh per metric ton of metallic iron, on basis of athermal efficiency of 85%.

For the production of 20 metric tons of steel per hour 27 920 kg ore andan electrical energy of 5494 kWh are necessary as well as a transformerhaving at least a power of 5,77 MW.

The shaft furnace has an interior diameter of 2,5 m. The height of thereduction zone amounts to 8 m, while the melting zone has a height of 2m. The molten material forms a bath having a depth of 200 mm.

The liquid material produced by the melting of the pellets must bealloyed in order to get a steel quality of 0,15% C, 0,60% Mn, 0,20% Siand 0,03% Al. These alloying elements are:

0,7 kg coal per metric ton of steel Without further analysis, theforegoing will so fully reveal the gist of the present invention thatothers can by applying current knowledge readily adapt it for variousapplications without omitting features that, from the standpoint ofprior art, fairly constitute essential characteristics of the generic orspecific aspects of this invention and, therefore, such adaptationsshould and are intended to be comprehended within the meaning and rangeof equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended l. A process for the production of steel froma material selected from the group consisting of ore, pellets, andsinter comprising the steps of admitting a charge into a substantiallyvertically arranged zone so as to form in said zone a column of saidcharge which descends by gravity from an upper portion to a lowerportion of said zone; reducing at least part of said charge in theregion of said upper portion of said zone; melting said charge in theregion of said lower portion of said zone with an electric are directedat the lower portion of said column; superheating the resulting moltenmaterial with said arc; and evacuating the superheated molten materialfrom said zone substantially continuously during the melting step.

2. A process as defined in claim 1, wherein said zone has anapproximately constant cross-sectional area.

3. A process as defined in claim 2, wherein said zone is of slightlydownwardly and outwardly tapering configuration.

4. A process as defined in claim 1, wherein said are heats and melts themajor part of the cross-section of said leading end.

5. A process as defined in claim 1, wherein said arc is substantiallycentered with respect to the crosssection of said leading end.

6. A process as defined in claim 1, said zone having a bottom; andwherein said arc is effective for forming an approximately dome-shapedcavity in said leading end so that only a peripheral portion of saidleading end bears against said bottom to support said column in saidzone.

7. A process as defined in claim I, wherein the melting step isperformed substantially continuously.

8. A process as defined in claim 1, wherein the reducing step comprisesintroducing a reducing gas into said zone.

9. A process as defined in claim 8, wherein at least part of saidreducing gas is introduced directly into said upper portion of said zonefrom peripherally of said zone.

10. A process as defined in claim 8, wherein at least part of saidreducing gas is introduced into said lower portion of said zone to beheated by said are.

11. A process as defined in claim 8, wherein the melting capacity ofsaid arc is variable in response to changes in the quantity ofelectrical energy supplied for said are and the quantity of saidreducing gas introduced into said zone varies in response to saidchanges.

12. A process as defined in claim 8; and further comprising the step ofintroducing an inert gas into said zone for maintaining reducingconditions in said zone.

13. A process as defined in claim 1, wherein the admitting step isperformed substantially continuously.

14. A process as defined in claim 1, wherein said charge comprisesalloying additions so that said molten material is in the form of steelhaving a desired analysis.

15. A process as defined in claim 14, wherein said alloying additionsare at least partially in the form of reducible oxides.

16. A process as defined in claim 1, wherein said charge compriseslimestone.

17. A process as defined in claim 1, wherein said charge comprises coke.

18. A process as defined in claim 1, said charge comprising additionsfor influencing the nature of said molten material; and wherein saidadditives are substantially uniformly distributed throughout saidcharge.

19. A process as defined in claim 1, wherein the melting step isperformed under substantially non-oxidizing conditions.

20. A process as defined in claim 1, wherein, the superheating stepcomprises temporarily collecting said molten material in said lowerportion of said zone.

1. A process for the production of steel from a material selected fromthe group consisting of ore, pellets, and sinter comprising the steps ofadmitting a charge into a substantially vertically arranged zone so asto form in said zone a column of said charge which descends by gravityfrom an upper portion to a lower portion of said zone; reducing at leastpart of said charge in the region of said upper portion of said zone;melting said charge in the region of said lower portion of said zonewith an electric arc directed at the lower portion of said column;superheating the resulting molten material with said arc; and evacuatingthe superheated molten material from said zone substantiallycontinuously during the melting step.
 2. A process as defined in claim1, wherein said zone has an approximately constant cross-sectional area.3. A process as defined in claim 2, wherein said zone is of slightlydownwardly and outwardly tapering configuration.
 4. A process as definedin claim 1, wherein said arc heats and melts the major part of thecross-section of said leading end.
 5. A process as defined in claim 1,wherein said arc is substantially centered with respect to thecross-section of said leading end.
 6. A process as defined in claim 1,said zone having a bottom; and wherein said arc is effective for formingan approximately dome-shaped cavity in said leading end so that only aperipheral portion of said leading end bears against said bottom tosupport said column in said zone.
 7. A process as defined in claim 1,wherein the melting step is performed substantially continuously.
 8. Aprocess as defined in claim 1, wherein the reducing step comprisesintroducing a reducing gas into said zone.
 9. A process as defined inclaim 8, wherein at least part of said reducing gas is introduceddirectly into said upper portion of said zone from peripherally of saidzone.
 10. A process as defined in claim 8, wherein at least part of saidreducing gas is introduced into said lower portion of said zone to beheated by said arc.
 11. A process as defined in claim 8, wherein themelting capacity of said arc is variable in response to changes in thequantity of electrical energy supplied for said arc and the quantity ofsaid reducing gas introduced into said zone varies in response to saidchanges.
 12. A process as defined in claim 8; and further comprising thestep of introducing an inert gas into said zone for maintaining reducingconditions in said zone.
 13. A process as defined in claim 1, whereinthe admitting step is performed substantially continuously.
 14. Aprocess as defined in claim 1, wherein said charge comprises alloyingadditions so that said molten material is in the form of steel having adesired analysis.
 15. A process as defined in claim 14, wherein saidalloying additions are at least partially in the form of reducibleoxides.
 16. A process as defined in claim 1, wherein said chargecomprises limestone.
 17. A process as defined in claim 1, wherein saidcharge comprises coke.
 18. A process as defined in claim 1, said chargecomprising additions for influencing the nature of said molten material;and wherein said additives are substantially uniformly distributedthroughout said charge.
 19. A PROCESS AS DEFINED IN CLAIM 1, WHEREIN THEMELTING STEP IS PERFORMED UNDER SUBSTANTIALLY NON-OXIDIZING CONDITIONS.20. A process as defined in claim 1, wherein, the superheating stepcomprises temporarily collecting said molten material in said lowerportion of said zone.